diff --git a/app/game-api/src/realtime/authenticatedConnection.ts b/app/game-api/src/realtime/authenticatedConnection.ts
new file mode 100644
index 00000000..da0bb12f
--- /dev/null
+++ b/app/game-api/src/realtime/authenticatedConnection.ts
@@ -0,0 +1,86 @@
+import type { ServerResponse } from 'node:http';
+import type { GameSessionTokenPayload } from '@sammo-ts/common/auth/gameToken';
+
+const MAX_PENDING_FRAMES = 32;
+const MAX_BUFFER_BYTES = 64 * 1024;
+
+/** Revalidate before work and before writing its result; never retain unbounded frames. */
+export class AuthenticatedRealtimeConnection {
+    private queue = Promise.resolve();
+    private pending = 0;
+    private ended = false;
+    private readonly expiryTimer: ReturnType<typeof setTimeout>;
+    private cleanup = new Set<() => void>();
+
+    constructor(
+        readonly auth: GameSessionTokenPayload,
+        private readonly response: ServerResponse,
+        private readonly resolveAuth: () => Promise<GameSessionTokenPayload | null>
+    ) {
+        // AccessTokenStore requires a full remaining TTL second on every lookup.
+        this.expiryTimer = setTimeout(() => this.close(), Math.max(0, Date.parse(auth.expiresAt) - Date.now() - 999));
+        this.expiryTimer.unref();
+        response.once('close', this.close);
+        response.once('error', this.close);
+    }
+
+    get closed(): boolean {
+        return this.ended;
+    }
+
+    onClose(cleanup: () => void): void {
+        if (this.ended) cleanup();
+        else this.cleanup.add(cleanup);
+    }
+
+    private async currentAuth(): Promise<GameSessionTokenPayload | null> {
+        if (this.ended) return null;
+        const current = await this.resolveAuth();
+        if (
+            !current ||
+            this.ended ||
+            current.sessionId !== this.auth.sessionId ||
+            current.user.id !== this.auth.user.id ||
+            current.profile !== this.auth.profile
+        ) {
+            this.close();
+            return null;
+        }
+        return current;
+    }
+
+    enqueue(work: (auth: GameSessionTokenPayload) => Promise<string | null>): void {
+        if (this.ended) return;
+        if (this.pending >= MAX_PENDING_FRAMES || this.response.writableLength > MAX_BUFFER_BYTES) {
+            this.close();
+            return;
+        }
+        this.pending += 1;
+        this.queue = this.queue
+            .then(async () => {
+                const current = await this.currentAuth();
+                if (!current) return;
+                const frame = await work(current);
+                if (!frame || !(await this.currentAuth())) return;
+                if (Buffer.byteLength(frame) > MAX_BUFFER_BYTES || !this.response.write(frame)) this.close();
+            })
+            .catch(() => {
+                // Redis/auth failure is fail closed. Reconnect must authenticate again.
+                this.close();
+            })
+            .finally(() => {
+                this.pending -= 1;
+            });
+    }
+
+    close = (): void => {
+        if (this.ended) return;
+        this.ended = true;
+        clearTimeout(this.expiryTimer);
+        this.response.off('close', this.close);
+        this.response.off('error', this.close);
+        for (const cleanup of this.cleanup) cleanup();
+        this.cleanup.clear();
+        if (!this.response.destroyed && !this.response.writableEnded) this.response.end();
+    };
+}
diff --git a/app/game-api/src/server.ts b/app/game-api/src/server.ts
index c82830c7..8adeb378 100644
--- a/app/game-api/src/server.ts
+++ b/app/game-api/src/server.ts
@@ -1,3 +1,4 @@
+import { safeHttpLoggerOptions, safeHttpErrorHandler } from '@sammo-ts/common';
 import fastify, { type FastifyRequest } from 'fastify';
 import cors from '@fastify/cors';
 import fastifyStatic from '@fastify/static';
@@ -32,6 +33,8 @@ import { appRouter } from './router.js';
 import { buildBattleSimQueueKeys } from './battleSim/keys.js';
 import { RedisBattleSimTransport } from './battleSim/redisTransport.js';
 import { RedisRealtimeEventHub } from './realtime/eventHub.js';
+import { isGameAccessBlocked } from '@sammo-ts/common/auth/sanctions';
+import { AuthenticatedRealtimeConnection } from './realtime/authenticatedConnection.js';
 import { formatSseFrame } from './realtime/sse.js';
 import {
     shouldForwardRealtimeEvent,
@@ -99,11 +102,16 @@ export const createGameApiServer = async () => {
         imageUploadSecret
     );
     const app = fastify({
-        logger: true,
+        logger: safeHttpLoggerOptions,
         routerOptions: {
             maxParamLength: 2048,
         },
     });
+    app.setErrorHandler(safeHttpErrorHandler);
+    const realtimeConnections = new Set<AuthenticatedRealtimeConnection>();
+    app.addHook('preClose', async () => {
+        for (const connection of realtimeConnections) connection.close();
+    });
     const postgres = createGamePostgresConnector(resolvePostgresConfigFromEnv({ schema: config.profile }));
     const redis = createRedisConnector(resolveRedisConfigFromEnv());
 
@@ -150,6 +158,12 @@ export const createGameApiServer = async () => {
         config.flushChannel,
         flushStore,
         async (event) => {
+            const flushedAt = Date.parse(event.flushedAt);
+            for (const connection of realtimeConnections) {
+                if (connection.auth.user.id === event.userId && Date.parse(connection.auth.issuedAt) <= flushedAt) {
+                    connection.close();
+                }
+            }
             await Promise.all([iconFlushHandler(event), identityFlushHandler(event)]);
         },
         (error, event) => {
@@ -299,14 +313,24 @@ export const createGameApiServer = async () => {
         },
     });
 
+    const resolveRealtimeAuth = async (token: string | null): Promise<GameSessionTokenPayload | null> => {
+        const auth = await resolveAuthFromToken(token, accessTokenStore, flushStore);
+        if (
+            !auth ||
+            auth.profile !== config.profileName ||
+            isGameAccessBlocked(auth.sanctions, [config.profileName, config.profile])
+        )
+            return null;
+        return auth;
+    };
+
     app.get(config.eventsPath, async (request, reply) => {
         const query = request.query as { token?: string; scope?: string };
         const subscriptionScope = query.scope === 'tournament' ? 'tournament' : 'dashboard';
         const tokenFromHeader = extractBearerToken(request.headers.authorization);
-        const tokenFromQuery = typeof query.token === 'string' ? query.token : null;
-        const auth = await resolveAuthFromToken(tokenFromHeader ?? tokenFromQuery, accessTokenStore, flushStore);
+        const auth = query.token === undefined ? await resolveRealtimeAuth(tokenFromHeader) : null;
 
-        if (!auth) {
+        if (!auth || auth.profile !== config.profileName) {
             await reply.status(401).send({ ok: false, error: 'unauthorized' });
             return;
         }
@@ -351,88 +375,62 @@ export const createGameApiServer = async () => {
         reply.raw.setTimeout?.(0);
         reply.raw.flushHeaders?.();
 
-        const sendFrame = (payload: string) => {
-            try {
-                reply.raw.write(payload);
-            } catch {
-                return;
-            }
-        };
-
-        sendFrame(
-            formatSseFrame({
-                event: 'ready',
-                data: '{}',
-            })
+        const connection = new AuthenticatedRealtimeConnection(auth, reply.raw, () =>
+            resolveRealtimeAuth(tokenFromHeader)
         );
-
-        let closed = false;
-        let eventQueue = Promise.resolve();
+        realtimeConnections.add(connection);
+        connection.onClose(() => {
+            realtimeConnections.delete(connection);
+        });
+        connection.enqueue(async () => formatSseFrame({ event: 'ready', data: '{}' }));
         const unsubscribe = realtimeHub.subscribe((event) => {
             if (!shouldForwardRealtimeEvent(event, subscriptionScope)) return;
-            eventQueue = eventQueue
-                .then(async () => {
-                    if (closed) return;
-                    const identities = [viewerIdentity];
-                    if (shouldReloadRealtimeViewerIdentity(event, viewerIdentity)) {
-                        const nextIdentity = await loadViewerIdentity();
-                        identities.push(nextIdentity);
-                        viewerIdentity = nextIdentity;
-                    }
-                    let refreshGrant: string | undefined;
-                    const publicEvent = toPublicRealtimeEvent(event, identities, () => {
-                        refreshGrant ??= createRealtimeAccessGrant(auth, config.profileName, config.gameTokenSecret);
-                        return refreshGrant;
-                    });
-                    if (!publicEvent || closed) return;
-                    if (refreshGrant) {
-                        try {
-                            await registerRealtimeAccessGrant(redis.client, refreshGrant, config.profileName);
-                        } catch {
-                            // Preserve the invalidation. An unregistered grant safely falls back
-                            // to the normal scored refresh path.
-                        }
-                    }
-                    sendFrame(
-                        formatSseFrame({
-                            event: publicEvent.type,
-                            data: JSON.stringify(publicEvent),
-                        })
-                    );
-                })
-                .catch(() => {
-                    // A best-effort notification must not affect committed game state.
+            connection.enqueue(async (currentAuth) => {
+                const identities = [viewerIdentity];
+                if (shouldReloadRealtimeViewerIdentity(event, viewerIdentity)) {
+                    const nextIdentity = await loadViewerIdentity();
+                    identities.push(nextIdentity);
+                    viewerIdentity = nextIdentity;
+                }
+                let refreshGrant: string | undefined;
+                const publicEvent = toPublicRealtimeEvent(event, identities, () => {
+                    refreshGrant ??= createRealtimeAccessGrant(currentAuth, config.profileName, config.gameTokenSecret);
+                    return refreshGrant;
                 });
+                if (!publicEvent || connection.closed) return null;
+                if (refreshGrant) {
+                    try {
+                        await registerRealtimeAccessGrant(redis.client, refreshGrant, config.profileName);
+                    } catch {
+                        // An unregistered grant falls back to the scored refresh path.
+                    }
+                }
+                return formatSseFrame({ event: publicEvent.type, data: JSON.stringify(publicEvent) });
+            });
         });
-
+        connection.onClose(unsubscribe);
         let heartbeatPending = false;
         const heartbeat = setInterval(() => {
-            if (heartbeatPending) return;
+            if (heartbeatPending || connection.closed) return;
             heartbeatPending = true;
-            void turnEngineStatus
-                .get()
-                .then((turnEngineRunning) => {
-                    if (closed) return;
-                    sendFrame(
-                        formatSseFrame({
-                            event: 'ping',
-                            data: JSON.stringify({ turnEngineRunning }),
-                        })
-                    );
-                })
-                .finally(() => {
+            connection.enqueue(async () => {
+                try {
+                    return formatSseFrame({
+                        event: 'ping',
+                        data: JSON.stringify({ turnEngineRunning: await turnEngineStatus.get() }),
+                    });
+                } finally {
                     heartbeatPending = false;
-                });
-        }, 15000);
-
-        const close = () => {
-            closed = true;
+                }
+            });
+        }, 15_000);
+        connection.onClose(() => {
             clearInterval(heartbeat);
-            unsubscribe();
-        };
-
-        request.raw.on('close', close);
-        request.raw.on('aborted', close);
+        });
+        request.raw.once('aborted', connection.close);
+        connection.onClose(() => {
+            request.raw.off('aborted', connection.close);
+        });
     });
 
     app.get('/healthz', async (_request, reply) => {
diff --git a/app/game-api/src/trpc.ts b/app/game-api/src/trpc.ts
index 1745bfbd..d479cbea 100644
--- a/app/game-api/src/trpc.ts
+++ b/app/game-api/src/trpc.ts
@@ -1,3 +1,4 @@
+import { safeTrpcErrorFormatter } from '@sammo-ts/common';
 import { randomUUID } from 'node:crypto';
 import { initTRPC, TRPCError } from '@trpc/server';
 import { middlewareMarker } from '@trpc/server/unstable-core-do-not-import';
@@ -20,7 +21,7 @@ import {
 import { getDeferredGeneralAccessLimit } from './services/deferredGeneralAccess.js';
 import { recordGeneralActivity } from './services/generalActivity.js';
 
-const t = initTRPC.context<GameApiContext>().create();
+const t = initTRPC.context<GameApiContext>().create({ errorFormatter: safeTrpcErrorFormatter });
 
 const requireAuthMiddleware = t.middleware(({ ctx, next }) => {
     if (!ctx.auth) {
diff --git a/app/game-api/test/authenticatedRealtimeConnection.test.ts b/app/game-api/test/authenticatedRealtimeConnection.test.ts
new file mode 100644
index 00000000..0dda5784
--- /dev/null
+++ b/app/game-api/test/authenticatedRealtimeConnection.test.ts
@@ -0,0 +1,95 @@
+import { PassThrough } from 'node:stream';
+import type { ServerResponse } from 'node:http';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import type { GameSessionTokenPayload } from '@sammo-ts/common/auth/gameToken';
+import { AuthenticatedRealtimeConnection } from '../src/realtime/authenticatedConnection.js';
+
+const payload = (): GameSessionTokenPayload => ({
+    version: 1,
+    sessionId: 'test-session',
+    profile: 'che:default',
+    issuedAt: new Date().toISOString(),
+    expiresAt: new Date(Date.now() + 60_000).toISOString(),
+    user: {
+        id: 'test-user',
+        username: 'test',
+        displayName: 'test',
+        roles: ['user'],
+        createdAt: new Date().toISOString(),
+    },
+    sanctions: {},
+});
+const fixture = (resolve: () => Promise<GameSessionTokenPayload | null>, auth = payload()) => {
+    const response = new PassThrough();
+    const frames: string[] = [];
+    response.on('data', (chunk) => frames.push(String(chunk)));
+    const connection = new AuthenticatedRealtimeConnection(auth, response as unknown as ServerResponse, resolve);
+    return { response, frames, connection };
+};
+afterEach(() => vi.useRealTimers());
+
+describe('authenticated realtime connection', () => {
+    it('does not forward an in-flight result after the token is revoked during its work', async () => {
+        const auth = payload();
+        let current: GameSessionTokenPayload | null = auth;
+        const { connection, frames } = fixture(async () => current, auth);
+        connection.enqueue(async () => {
+            current = null;
+            return 'private invalidation';
+        });
+        await vi.waitFor(() => expect(connection.closed).toBe(true));
+        expect(frames).toEqual([]);
+    });
+    it.each(['sessionId', 'profile'] as const)('rejects a replacement %s even for the same user', async (field) => {
+        const auth = payload();
+        const { connection, frames } = fixture(async () => ({ ...auth, [field]: 'replacement' }), auth);
+        connection.enqueue(async () => 'private invalidation');
+        await vi.waitFor(() => expect(connection.closed).toBe(true));
+        expect(frames).toEqual([]);
+    });
+    it('fails closed when authentication storage fails', async () => {
+        const { connection, frames } = fixture(async () => {
+            throw new Error('redis unavailable');
+        });
+        connection.enqueue(async () => 'private invalidation');
+        await vi.waitFor(() => expect(connection.closed).toBe(true));
+        expect(frames).toEqual([]);
+    });
+    it('ends an idle expired stream and releases subscriptions only once', async () => {
+        vi.useFakeTimers();
+        const auth = payload();
+        const { connection } = fixture(async () => auth, auth);
+        const cleanup = vi.fn();
+        connection.onClose(cleanup);
+        await vi.advanceTimersByTimeAsync(60_001);
+        expect(connection.closed).toBe(true);
+        expect(cleanup).toHaveBeenCalledTimes(1);
+        connection.close();
+        expect(cleanup).toHaveBeenCalledTimes(1);
+    });
+    it('bounds queued work while an earlier event is blocked', async () => {
+        const auth = payload();
+        const { connection, frames } = fixture(async () => auth, auth);
+        let release!: () => void;
+        const waiting = new Promise<void>((resolve) => {
+            release = resolve;
+        });
+        connection.enqueue(async () => {
+            await waiting;
+            return 'private invalidation';
+        });
+        for (let i = 0; i < 100; i += 1) connection.enqueue(async () => 'private invalidation');
+        expect(connection.closed).toBe(true);
+        release();
+        await new Promise((resolve) => setTimeout(resolve, 0));
+        expect(frames).toEqual([]);
+    });
+    it('ends a slow socket instead of retaining further frames', async () => {
+        const auth = payload();
+        const { connection, response } = fixture(async () => auth, auth);
+        response.write = vi.fn(() => false);
+        connection.enqueue(async () => 'event: ping\ndata: {}\n\n');
+        await vi.waitFor(() => expect(connection.closed).toBe(true));
+        expect(response.writableEnded).toBe(true);
+    });
+});
diff --git a/app/game-api/test/httpErrorPrivacy.test.ts b/app/game-api/test/httpErrorPrivacy.test.ts
new file mode 100644
index 00000000..1b75cf1c
--- /dev/null
+++ b/app/game-api/test/httpErrorPrivacy.test.ts
@@ -0,0 +1,51 @@
+import fastify from 'fastify';
+import { TRPCError } from '@trpc/server';
+import { fastifyTRPCPlugin } from '@trpc/server/adapters/fastify';
+import { describe, expect, it } from 'vitest';
+import { router as gameRouter, sessionActivityProcedure } from '../src/trpc.js';
+
+const internalFailure = () => {
+    throw new Error('synthetic-db-secret', { cause: new Error('synthetic-cause-secret') });
+};
+const badInput = () => {
+    throw new TRPCError({
+        code: 'BAD_REQUEST',
+        message: '잘못된 입력입니다.',
+        cause: new Error('synthetic-private-cause'),
+    });
+};
+
+describe('public HTTP error privacy', () => {
+    it('the real router factory hides internal errors and all stacks while preserving validation messages', async () => {
+        const app = fastify();
+        await app.register(fastifyTRPCPlugin, {
+            prefix: '/game',
+            trpcOptions: {
+                router: gameRouter({
+                    internal: sessionActivityProcedure.query(internalFailure),
+                    invalid: sessionActivityProcedure.query(badInput),
+                }),
+                createContext: () => ({}),
+            },
+        });
+        try {
+            const address = await app.listen({ host: '127.0.0.1', port: 0 });
+            for (const prefix of ['game']) {
+                for (const procedure of ['internal', 'invalid']) {
+                    const response = await fetch(`${address}/${prefix}/${procedure}`);
+                    const body = (await response.json()) as {
+                        error: { message: string; data: { code: string; stack?: string } };
+                    };
+                    expect(response.status).toBe(procedure === 'internal' ? 500 : 400);
+                    expect(body.error.message).toBe(
+                        procedure === 'internal' ? 'Internal server error' : '잘못된 입력입니다.'
+                    );
+                    expect(body.error.data.stack).toBeUndefined();
+                    expect(JSON.stringify(body)).not.toContain('synthetic-');
+                }
+            }
+        } finally {
+            await app.close();
+        }
+    });
+});
diff --git a/app/game-api/test/safeHttpLogger.test.ts b/app/game-api/test/safeHttpLogger.test.ts
new file mode 100644
index 00000000..2ee0f89b
--- /dev/null
+++ b/app/game-api/test/safeHttpLogger.test.ts
@@ -0,0 +1,46 @@
+import { Writable } from 'node:stream';
+import fastify from 'fastify';
+import { describe, expect, it } from 'vitest';
+import { safeHttpLoggerOptions, safeHttpErrorHandler } from '@sammo-ts/common';
+
+describe('HTTP log credential boundaries', () => {
+    it('logs static routes/status but no query, unmatched path, header, body, stack or cause secrets', async () => {
+        let output = '';
+        const stream = new Writable({
+            write(chunk, _encoding, done) {
+                output += String(chunk);
+                done();
+            },
+        });
+        const app = fastify({ logger: { ...safeHttpLoggerOptions, stream } });
+        app.setErrorHandler(safeHttpErrorHandler);
+        app.post('/events', async () => {
+            throw Object.assign(new Error('synthetic-error-secret', { cause: new Error('synthetic-cause-secret') }), {
+                code: 'P2002',
+                detail: 'synthetic-detail-secret',
+            });
+        });
+        try {
+            const address = await app.listen({ host: '127.0.0.1', port: 0 });
+            const response = await fetch(`${address}/events?token=synthetic-query-secret`, {
+                method: 'POST',
+                headers: { authorization: 'Bearer synthetic-header-secret', 'content-type': 'application/json' },
+                body: JSON.stringify({ password: 'synthetic-body-secret' }),
+            });
+            expect(await response.json()).toMatchObject({ message: 'Internal server error' });
+            await fetch(`${address}/synthetic-path-secret`);
+            const logs = output
+                .trim()
+                .split('\n')
+                .map((line) => JSON.parse(line));
+            expect(logs.some((entry) => entry.req?.url === '/events')).toBe(true);
+            expect(logs.some((entry) => entry.res?.statusCode === 500)).toBe(true);
+            expect(logs.some((entry) => entry.err?.code === 'P2002')).toBe(true);
+            for (const field of ['query', 'header', 'body', 'error', 'cause', 'detail', 'path']) {
+                expect(output).not.toContain(`synthetic-${field}-secret`);
+            }
+        } finally {
+            await app.close();
+        }
+    });
+});
diff --git a/app/game-api/test/securityTransport.integration.test.ts b/app/game-api/test/securityTransport.integration.test.ts
index 2e00a6a5..e869dd79 100644
--- a/app/game-api/test/securityTransport.integration.test.ts
+++ b/app/game-api/test/securityTransport.integration.test.ts
@@ -1,3 +1,4 @@
+import { buildGameEventChannel } from '@sammo-ts/common';
 import { createHash } from 'node:crypto';
 import { projectCurrentGeneral } from '../src/router/playAudit/projection.js';
 import { asRecord } from '@sammo-ts/common';
@@ -2317,9 +2318,51 @@ integration('game API security over HTTP transport', () => {
                     {
                         decisionId: decisionIds[0]!,
                         ordinal: 0,
-                        steps: Array.from({ length: 128 }, (_, sequence) => sequence === 127
-                            ? { ...step, sequence, kind: 'DECISION_START', reservedAction: '휴식', effectivePolicy: {"schemaVersion":1,"general":{"priority":["징병"],"flags":{"징병":true,"출병":false}},"nation":{"priority":["천도"],"flags":{"천도":true},"values":{"reqNationGold":4321,"reqNationRice":100,"reqHumanWarUrgentGold":100,"reqHumanWarUrgentRice":100,"reqHumanWarRecommandGold":100,"reqHumanWarRecommandRice":100,"reqHumanDevelGold":100,"reqHumanDevelRice":100,"reqNpcWarGold":100,"reqNpcWarRice":100,"reqNpcDevelGold":100,"reqNpcDevelRice":100,"minimumResourceActionAmount":100,"maximumResourceActionAmount":100,"minNpcWarLeadership":100,"minWarCrew":100,"minNpcRecruitCityPopulation":100,"safeRecruitCityPopulationRatio":100,"properWarTrainAtmos":100,"cureThreshold":100},"combatForce":{"1":[2,3]},"supportForce":[4],"developForce":[5],"secret":"decision-secret"},"secret":"decision-secret"} }
-                            : ({ ...step, sequence })),
+                        steps: Array.from({ length: 128 }, (_, sequence) =>
+                            sequence === 127
+                                ? {
+                                      ...step,
+                                      sequence,
+                                      kind: 'DECISION_START',
+                                      reservedAction: '휴식',
+                                      effectivePolicy: {
+                                          schemaVersion: 1,
+                                          general: { priority: ['징병'], flags: { 징병: true, 출병: false } },
+                                          nation: {
+                                              priority: ['천도'],
+                                              flags: { 천도: true },
+                                              values: {
+                                                  reqNationGold: 4321,
+                                                  reqNationRice: 100,
+                                                  reqHumanWarUrgentGold: 100,
+                                                  reqHumanWarUrgentRice: 100,
+                                                  reqHumanWarRecommandGold: 100,
+                                                  reqHumanWarRecommandRice: 100,
+                                                  reqHumanDevelGold: 100,
+                                                  reqHumanDevelRice: 100,
+                                                  reqNpcWarGold: 100,
+                                                  reqNpcWarRice: 100,
+                                                  reqNpcDevelGold: 100,
+                                                  reqNpcDevelRice: 100,
+                                                  minimumResourceActionAmount: 100,
+                                                  maximumResourceActionAmount: 100,
+                                                  minNpcWarLeadership: 100,
+                                                  minWarCrew: 100,
+                                                  minNpcRecruitCityPopulation: 100,
+                                                  safeRecruitCityPopulationRatio: 100,
+                                                  properWarTrainAtmos: 100,
+                                                  cureThreshold: 100,
+                                              },
+                                              combatForce: { '1': [2, 3] },
+                                              supportForce: [4],
+                                              developForce: [5],
+                                              secret: 'decision-secret',
+                                          },
+                                          secret: 'decision-secret',
+                                      },
+                                  }
+                                : { ...step, sequence }
+                        ),
                     },
                     {
                         decisionId: decisionIds[0]!,
@@ -3530,6 +3573,108 @@ integration('game API security over HTTP transport', () => {
         }
     });
 
+    const openRealtime = async (accessToken: string) => {
+        const abort = new AbortController();
+        const response = await fetch(`${baseUrl}${server!.config.eventsPath}`, {
+            headers: { authorization: `Bearer ${accessToken}` },
+            signal: abort.signal,
+        });
+        expect(response.status).toBe(200);
+        expect(response.headers.get('content-type')).toBe('text/event-stream');
+        const reader = response.body!.getReader();
+        const ready = await reader.read();
+        expect(new TextDecoder().decode(ready.value)).toContain('event: ready');
+        return { abort, reader };
+    };
+
+    it('SSE accepts header auth and rejects query or cross-profile credentials', async () => {
+        const token = await createAccessToken('sse-query', {});
+        const queryOnly = await fetch(`${baseUrl}${server!.config.eventsPath}?token=${encodeURIComponent(token)}`);
+        expect(queryOnly.status).toBe(401);
+        const foreign = await accessTokenStore.create({ ...buildPayload('sse-foreign', {}), profile: 'other:default' });
+        if (!foreign) throw new Error('SSE foreign token fixture failed');
+        try {
+            const response = await fetch(`${baseUrl}${server!.config.eventsPath}`, {
+                headers: { authorization: `Bearer ${foreign.accessToken}` },
+            });
+            expect(response.status).toBe(401);
+            const stream = await openRealtime(token);
+            stream.abort.abort();
+        } finally {
+            await accessTokenStore.revoke(token);
+            await accessTokenStore.revoke(foreign.accessToken);
+        }
+    });
+
+    it.each([
+        { label: 'ban', sanctions: { bannedUntil: '2099-01-01T00:00:00.000Z' } },
+        { label: 'suspension', sanctions: { suspendedUntil: '2099-01-01T00:00:00.000Z' } },
+        {
+            label: 'profile game restriction',
+            sanctions: { serverRestrictions: { [profileName]: { blockedFeatures: ['game'] } } },
+        },
+    ])('SSE rejects $label before opening a stream', async ({ label, sanctions }) => {
+        const token = await createAccessToken(`sse-${label}`, sanctions);
+        try {
+            const response = await fetch(`${baseUrl}${server!.config.eventsPath}`, {
+                headers: { authorization: `Bearer ${token}` },
+            });
+            expect(response.status).toBe(401);
+            expect(response.headers.get('content-type')).not.toBe('text/event-stream');
+        } finally {
+            await accessTokenStore.revoke(token);
+        }
+    });
+
+    it('SSE closes on idle expiry without forwarding another frame', async () => {
+        const auth = { ...buildPayload('sse-expiry', {}), expiresAt: new Date(Date.now() + 3500).toISOString() };
+        const created = await accessTokenStore.create(auth);
+        if (!created) throw new Error('SSE expiry token fixture failed');
+        const stream = await openRealtime(created.accessToken);
+        try {
+            expect(await stream.reader.read()).toMatchObject({ done: true });
+            expect((await requestTrpc('general.me', { accessToken: created.accessToken })).response.status).toBe(401);
+        } finally {
+            stream.abort.abort();
+            await accessTokenStore.revoke(created.accessToken);
+        }
+    });
+
+    it('SSE rechecks a revoked token before forwarding a relevant event or refresh grant', async () => {
+        const accessToken = await createAccessToken('sse-revoke', {});
+        const stream = await openRealtime(accessToken);
+        const channel = server!.config.profileName;
+        try {
+            const event = JSON.stringify({ type: 'tournamentChanged' });
+            await redis!.client.publish(buildGameEventChannel(channel), event);
+            const valid = await stream.reader.read();
+            expect(new TextDecoder().decode(valid.value)).toContain('refreshGrant');
+            expect(await accessTokenStore.revoke(accessToken)).toBe(true);
+            await redis!.client.publish(buildGameEventChannel(channel), event);
+            expect(await stream.reader.read()).toMatchObject({ done: true });
+        } finally {
+            stream.abort.abort();
+            await accessTokenStore.revoke(accessToken);
+        }
+    });
+
+    it('SSE closes an idle flushed user immediately without waiting for heartbeat', async () => {
+        const sseUser = `security-http-sse-flush-${process.pid}`;
+        const created = await accessTokenStore.create(buildPayload('sse-flush', {}, sseUser));
+        if (!created) throw new Error('SSE flush fixture failed');
+        const stream = await openRealtime(created.accessToken);
+        try {
+            await redis!.client.publish(
+                `${redisPrefix}:flush`,
+                JSON.stringify({ userId: sseUser, flushedAt: new Date().toISOString() })
+            );
+            expect(await stream.reader.read()).toMatchObject({ done: true });
+        } finally {
+            stream.abort.abort();
+            await accessTokenStore.revoke(created.accessToken);
+        }
+    });
+
     // Flush invalidates every token issued before the user watermark. Keep it
     // last so this lifecycle assertion cannot invalidate the actor tokens used
     // by the transport authorization matrix above.
diff --git a/app/game-frontend/e2e/mainNavigation.spec.ts b/app/game-frontend/e2e/mainNavigation.spec.ts
index e40ccf26..435dda0e 100644
--- a/app/game-frontend/e2e/mainNavigation.spec.ts
+++ b/app/game-frontend/e2e/mainNavigation.spec.ts
@@ -880,56 +880,66 @@ const installFixture = async (page: Page | BrowserContext, state: NavigationFixt
 
 const installRealtimeHarness = async (page: Page) => {
     await page.addInitScript(() => {
-        class TestEventSource extends EventTarget {
-            static latest: TestEventSource | null = null;
-            static created = 0;
-            static closed = 0;
-            readonly url: string;
-
-            constructor(url: string | URL) {
-                super();
-                this.url = url.toString();
-                TestEventSource.created += 1;
-                TestEventSource.latest = this;
-                queueMicrotask(() => this.dispatchEvent(new Event('open')));
-            }
-
-            close() {
-                if (TestEventSource.latest === this) {
-                    TestEventSource.latest = null;
-                    TestEventSource.closed += 1;
-                }
-            }
-        }
-
-        Object.defineProperty(window, 'EventSource', { configurable: true, value: TestEventSource });
-        Object.defineProperty(window, '__emitMainRealtime', {
-            configurable: true,
-            value: (type: string, payload: unknown) => {
-                TestEventSource.latest?.dispatchEvent(
-                    new MessageEvent(type, {
-                        data: JSON.stringify({
-                            type,
-                            ...(type === 'readModelInvalidated' || type === 'messagesInvalidated'
-                                ? { refreshGrant: 'fixture-realtime-grant' }
-                                : {}),
-                            ...((payload as object) ?? {}),
-                        }),
-                    })
-                );
+        const originalFetch = window.fetch.bind(window);
+        let latest: { emit: (type: string, payload: unknown) => void; close: () => void } | null = null;
+        let created = 0;
+        let closed = 0;
+        let authenticated = false;
+        let credentialInUrl = false;
+        window.fetch = (input, init) => {
+            const url = new URL(input instanceof Request ? input.url : String(input), location.href);
+            if (!url.pathname.endsWith('/events')) return originalFetch(input, init);
+            if (init?.signal?.aborted) return Promise.reject(new DOMException('Aborted', 'AbortError'));
+            authenticated = new Headers(init?.headers).get('authorization')?.startsWith('Bearer ga_') ?? false;
+            credentialInUrl = url.searchParams.has('token');
+            let controller!: ReadableStreamDefaultController<Uint8Array>;
+            let ended = false;
+            const source = {
+                close: () => {
+                    if (ended) return;
+                    ended = true;
+                    closed += 1;
+                    if (latest === source) latest = null;
+                    controller.close();
+                },
+                emit: (type: string, payload: unknown) => {
+                    if (ended) return;
+                    controller.enqueue(
+                        new TextEncoder().encode(
+                            `event: ${type}\ndata: ${JSON.stringify({
+                                type,
+                                ...(type === 'readModelInvalidated' || type === 'messagesInvalidated'
+                                    ? { refreshGrant: 'fixture-realtime-grant' }
+                                    : {}),
+                                ...((payload as object) ?? {}),
+                            })}\n\n`
+                        )
+                    );
+                },
+            };
+            const body = new ReadableStream<Uint8Array>({
+                start: (next) => {
+                    controller = next;
+                },
+                cancel: () => {
+                    if (!ended) {
+                        ended = true;
+                        closed += 1;
+                        if (latest === source) latest = null;
+                    }
+                },
+            });
+            created += 1;
+            latest = source;
+            init?.signal?.addEventListener('abort', source.close, { once: true });
+            return Promise.resolve(new Response(body, { headers: { 'content-type': 'text/event-stream' } }));
+        };
+        Object.assign(window, {
+            __emitMainRealtime: (type: string, payload: unknown) => {
+                latest?.emit(type, payload);
             },
-        });
-        Object.defineProperty(window, '__hasMainRealtime', {
-            configurable: true,
-            value: () => TestEventSource.latest !== null,
-        });
-        Object.defineProperty(window, '__mainRealtimeStats', {
-            configurable: true,
-            value: () => ({
-                active: TestEventSource.latest !== null,
-                created: TestEventSource.created,
-                closed: TestEventSource.closed,
-            }),
+            __hasMainRealtime: () => latest !== null,
+            __mainRealtimeStats: () => ({ active: latest !== null, created, closed, authenticated, credentialInUrl }),
         });
     });
 };
@@ -5430,10 +5440,53 @@ test('realtime read-model events skip clock-only work, merge bursts, patch in pl
             page.evaluate(() => (window as unknown as { __hasMainRealtime: () => boolean }).__hasMainRealtime())
         )
         .toBe(true);
+    expect(
+        await page.evaluate(() =>
+            (
+                window as unknown as {
+                    __mainRealtimeStats: () => { authenticated: boolean; credentialInUrl: boolean };
+                }
+            ).__mainRealtimeStats()
+        )
+    ).toMatchObject({ authenticated: true, credentialInUrl: false });
     await expect(page.locator('.tournament-status')).toHaveText('토너먼트: 경기 없음');
     await expect(page.locator('[data-navigation-id="tournament"]')).not.toHaveClass(/highlight/u);
     expect(state.dashboardGrantHeaders).toContain(null);
 
+    const captureRefreshLayout = async (phase: string): Promise<void> => {
+        if (!autoRefreshArtifactRoot) return;
+        await page.evaluate(() => document.fonts.ready);
+        const layout = await page.evaluate(() => ({
+            url: location.href,
+            viewport: { width: innerWidth, height: innerHeight, dpr: devicePixelRatio },
+            cards: Array.from(document.querySelectorAll('[data-main-target="general"], [data-main-target="city"]')).map(
+                (element) => {
+                    const style = getComputedStyle(element);
+                    return {
+                        target: element.getAttribute('data-main-target'),
+                        bounds: element.getBoundingClientRect().toJSON(),
+                        fontFamily: style.fontFamily,
+                        fontSize: style.fontSize,
+                        color: style.color,
+                        backgroundColor: style.backgroundColor,
+                        display: style.display,
+                    };
+                }
+            ),
+            images: Array.from(document.images).map((image) => ({
+                src: image.getAttribute('src'),
+                width: image.naturalWidth,
+                height: image.naturalHeight,
+                complete: image.complete,
+                objectFit: getComputedStyle(image).objectFit,
+            })),
+        }));
+        await Promise.all([
+            writeFile(resolve(autoRefreshArtifactRoot, `${phase}-layout.json`), JSON.stringify(layout, null, 2)),
+            writeFile(resolve(autoRefreshArtifactRoot, `${phase}-dom.html`), await page.content()),
+        ]);
+    };
+
     const operationsBeforeTournament = state.operations.length;
     state.stage = 1;
     await emitReadModelInvalidation(page, readModelInvalidation({ tournament: true }));
@@ -5473,6 +5526,7 @@ test('realtime read-model events skip clock-only work, merge bursts, patch in pl
         }).observe({ entryTypes: ['measure'] });
     });
 
+    await captureRefreshLayout('before-refresh');
     const callsBeforeRefresh = state.generalMeCalls;
     const operationsBeforeClockOnly = state.operations.length;
     await new Promise((resolve) => setTimeout(resolve, 300));
@@ -5616,6 +5670,7 @@ test('realtime read-model events skip clock-only work, merge bursts, patch in pl
             vueMeasures: probe.vueMeasures.filter((name) => /render|patch/u.test(name)),
         };
     });
+    await captureRefreshLayout('after-refresh');
     expect(profile.generalMounted).toBe(true);
     expect(profile.cityMounted).toBe(true);
     expect(profile.generalMutations).toBeGreaterThan(0);
diff --git a/app/game-frontend/e2e/tournamentBracket.spec.ts b/app/game-frontend/e2e/tournamentBracket.spec.ts
index 16eda4b3..1cc2dd08 100644
--- a/app/game-frontend/e2e/tournamentBracket.spec.ts
+++ b/app/game-frontend/e2e/tournamentBracket.spec.ts
@@ -371,37 +371,57 @@ const installFixture = async (
 
 const installFakeEventSource = async (page: Page) => {
     await page.addInitScript(() => {
-        class FakeEventSource extends EventTarget {
-            static instances: FakeEventSource[] = [];
-            readonly url: string;
-            closed = false;
-
-            constructor(url: string | URL) {
-                super();
-                this.url = String(url);
-                FakeEventSource.instances.push(this);
-                queueMicrotask(() => {
-                    if (!this.closed) this.dispatchEvent(new Event('open'));
-                });
-            }
-
-            close() {
-                this.closed = true;
-            }
-
-            emit(type: string, payload: unknown) {
-                if (this.closed) return;
-                this.dispatchEvent(new MessageEvent(type, { data: JSON.stringify(payload) }));
-            }
-        }
-
-        Object.defineProperty(window, 'EventSource', { configurable: true, value: FakeEventSource });
+        const originalFetch = window.fetch.bind(window);
+        const sources: Array<{
+            url: string;
+            closed: boolean;
+            authenticated: boolean;
+            emit: (type: string, payload: unknown) => void;
+        }> = [];
+        window.fetch = (input, init) => {
+            const url = new URL(input instanceof Request ? input.url : String(input), location.href);
+            if (!url.pathname.endsWith('/events')) return originalFetch(input, init);
+            if (init?.signal?.aborted) return Promise.reject(new DOMException('Aborted', 'AbortError'));
+            let controller!: ReadableStreamDefaultController<Uint8Array>;
+            const source = {
+                url: url.href,
+                closed: false,
+                authenticated: new Headers(init?.headers).get('authorization')?.startsWith('Bearer ga_') ?? false,
+                emit: (type: string, payload: unknown) => {
+                    if (!source.closed)
+                        controller.enqueue(
+                            new TextEncoder().encode(`event: ${type}\ndata: ${JSON.stringify(payload)}\n\n`)
+                        );
+                },
+            };
+            const body = new ReadableStream<Uint8Array>({
+                start: (next) => {
+                    controller = next;
+                },
+                cancel: () => {
+                    source.closed = true;
+                },
+            });
+            sources.push(source);
+            init?.signal?.addEventListener(
+                'abort',
+                () => {
+                    if (!source.closed) {
+                        source.closed = true;
+                        controller.close();
+                    }
+                },
+                { once: true }
+            );
+            return Promise.resolve(new Response(body, { headers: { 'content-type': 'text/event-stream' } }));
+        };
         Object.assign(window, {
-            __tournamentEventSourceCount: () => FakeEventSource.instances.filter((source) => !source.closed).length,
-            __tournamentEventSourceUrls: () =>
-                FakeEventSource.instances.filter((source) => !source.closed).map((source) => source.url),
+            __tournamentEventSourceCount: () => sources.filter((source) => !source.closed).length,
+            __tournamentEventSourceUrls: () => sources.filter((source) => !source.closed).map((source) => source.url),
+            __tournamentEventSourceAuthenticated: () =>
+                sources.filter((source) => !source.closed).every((source) => source.authenticated),
             __emitTournamentEvent: (type: string, payload: unknown) => {
-                for (const source of FakeEventSource.instances) source.emit(type, payload);
+                for (const source of sources) source.emit(type, payload);
             },
         });
     });
@@ -885,6 +905,18 @@ test('betting realtime refresh is shared across tabs and preserves local interac
     ).flat();
     expect(activeSourceUrls).toHaveLength(1);
     expect(new URL(activeSourceUrls[0]!).searchParams.get('scope')).toBe('tournament');
+    expect(new URL(activeSourceUrls[0]!).searchParams.has('token')).toBe(false);
+    for (const candidate of [page, follower]) {
+        expect(
+            await candidate.evaluate(() =>
+                (
+                    window as unknown as {
+                        __tournamentEventSourceAuthenticated: () => boolean;
+                    }
+                ).__tournamentEventSourceAuthenticated()
+            )
+        ).toBe(true);
+    }
 
     const before = {
         snapshot: operations.filter(({ operation }) => operation === 'tournament.getSnapshot').length,
diff --git a/app/game-frontend/package.json b/app/game-frontend/package.json
index 020ddced..27173c89 100644
--- a/app/game-frontend/package.json
+++ b/app/game-frontend/package.json
@@ -49,6 +49,7 @@
         "chart.js": "4.5.1",
         "date-fns": "^4.1.0",
         "es-toolkit": "^1.43.0",
+        "eventsource": "5.1.2",
         "mitt": "^3.0.1",
         "pinia": "^3.0.4",
         "tippy.js": "6.3.7",
diff --git a/app/game-frontend/src/stores/mainDashboard.ts b/app/game-frontend/src/stores/mainDashboard.ts
index 2c7f2678..fb3e938d 100644
--- a/app/game-frontend/src/stores/mainDashboard.ts
+++ b/app/game-frontend/src/stores/mainDashboard.ts
@@ -1,3 +1,4 @@
+import { createAuthenticatedEventSource, type AuthenticatedEventSource } from '../utils/authenticatedEventSource';
 import { receiveClockEngineState } from '../composables/useClockDisplay';
 import { computed, ref, toRaw, watch } from 'vue';
 import { defineStore } from 'pinia';
@@ -1139,16 +1140,15 @@ export const useMainDashboardStore = defineStore('mainDashboard', () => {
         }
     };
 
-    let realtimeSource: EventSource | null = null;
+    let realtimeSource: AuthenticatedEventSource | null = null;
     let realtimeToken: string | null = null;
     let visibilityListenerInstalled = false;
 
     const isAccessToken = (token: string | null): boolean => Boolean(token?.startsWith('ga_'));
 
-    const buildRealtimeUrl = (token: string): string => {
+    const buildRealtimeUrl = (): string => {
         const base = gameFrontendRuntimeConfig.gameSseUrl;
         const url = new URL(base, window.location.origin);
-        url.searchParams.set('token', token);
         return url.toString();
     };
 
@@ -1284,15 +1284,22 @@ export const useMainDashboardStore = defineStore('mainDashboard', () => {
         realtimeToken = token;
         realtimeStatus.value = 'idle';
 
-        const source = new EventSource(buildRealtimeUrl(token));
+        let needsRecovery = false;
+        const source = createAuthenticatedEventSource(buildRealtimeUrl(), token);
         realtimeSource = source;
 
         source.addEventListener('open', () => {
             markGameServerContact();
             realtimeStatus.value = 'connected';
             realtimeCoordinator?.postFromLeader({ kind: 'status', status: 'connected' });
+            if (needsRecovery) {
+                needsRecovery = false;
+                realtimeRefreshQueue.request();
+            }
         });
-        source.addEventListener('error', () => {
+        source.addEventListener('error', (event) => {
+            if (event.code === 401) void session.refreshGeneralStatus();
+            needsRecovery = true;
             realtimeStatus.value = realtimeEnabled.value ? 'idle' : 'paused';
             realtimeCoordinator?.postFromLeader({ kind: 'status', status: 'idle' });
         });
diff --git a/app/game-frontend/src/stores/tournamentPages.ts b/app/game-frontend/src/stores/tournamentPages.ts
index 18341c16..e0a00cee 100644
--- a/app/game-frontend/src/stores/tournamentPages.ts
+++ b/app/game-frontend/src/stores/tournamentPages.ts
@@ -1,3 +1,4 @@
+import { createAuthenticatedEventSource, type AuthenticatedEventSource } from '../utils/authenticatedEventSource';
 import { defineStore } from 'pinia';
 import { ref, watch } from 'vue';
 import type { PublicRealtimeEvent, TournamentViewInvalidation } from '@sammo-ts/common';
@@ -49,7 +50,7 @@ export const useTournamentPagesStore = defineStore('tournamentPages', () => {
     const realtimeStatus = ref<'idle' | 'connected'>('idle');
 
     let activeConsumers = 0;
-    let realtimeSource: EventSource | null = null;
+    let realtimeSource: AuthenticatedEventSource | null = null;
     let realtimeToken: string | null = null;
     let realtimeCoordinator: BroadcastTabCoordinator<TournamentTabMessage> | null = null;
     let realtimeCoordinatorScope: string | null = null;
@@ -136,10 +137,9 @@ export const useTournamentPagesStore = defineStore('tournamentPages', () => {
         if (!(await session.exchangeGatewayToken())) return null;
         return session.gameToken && isAccessToken(session.gameToken) ? session.gameToken : null;
     };
-    const buildRealtimeUrl = (token: string): string => {
+    const buildRealtimeUrl = (): string => {
         const base = gameFrontendRuntimeConfig.gameSseUrl;
         const url = new URL(base, window.location.origin);
-        url.searchParams.set('token', token);
         url.searchParams.set('scope', 'tournament');
         return url.toString();
     };
@@ -181,7 +181,7 @@ export const useTournamentPagesStore = defineStore('tournamentPages', () => {
         if (realtimeSource && realtimeToken === token) return;
         closeRealtimeSource();
         realtimeToken = token;
-        const source = new EventSource(buildRealtimeUrl(token));
+        const source = createAuthenticatedEventSource(buildRealtimeUrl(), token);
         realtimeSource = source;
         source.addEventListener('open', () => {
             realtimeStatus.value = 'connected';
@@ -196,7 +196,8 @@ export const useTournamentPagesStore = defineStore('tournamentPages', () => {
                 });
             }
         });
-        source.addEventListener('error', () => {
+        source.addEventListener('error', (event) => {
+            if (event.code === 401) void session.refreshGeneralStatus();
             needsRecovery = true;
             realtimeStatus.value = 'idle';
             realtimeCoordinator?.postFromLeader({ kind: 'status', status: 'idle' });
diff --git a/app/game-frontend/src/utils/authenticatedEventSource.ts b/app/game-frontend/src/utils/authenticatedEventSource.ts
new file mode 100644
index 00000000..fad692a3
--- /dev/null
+++ b/app/game-frontend/src/utils/authenticatedEventSource.ts
@@ -0,0 +1,26 @@
+import { EventSource } from 'eventsource';
+
+export type AuthenticatedEventSource = EventSource;
+
+/** Keep the access token out of browser/proxy URLs and ambient cookies. */
+export const createAuthenticatedEventSource = (url: string, accessToken: string): EventSource => {
+    const destination = new URL(url);
+    if (destination.searchParams.has('token') || destination.username || destination.password) {
+        throw new Error('Realtime credentials must use the authorization header.');
+    }
+    return new EventSource(destination, {
+        maxBufferSize: 64 * 1024,
+        fetch: (input, init) => {
+            const headers = new Headers(init?.headers);
+            headers.set('Authorization', `Bearer ${accessToken}`);
+            return fetch(input, {
+                ...init,
+                headers,
+                credentials: 'omit',
+                redirect: 'error',
+                cache: 'no-store',
+                referrerPolicy: 'no-referrer',
+            });
+        },
+    });
+};
diff --git a/app/game-frontend/test/authenticatedEventSource.test.ts b/app/game-frontend/test/authenticatedEventSource.test.ts
new file mode 100644
index 00000000..c23ee07c
--- /dev/null
+++ b/app/game-frontend/test/authenticatedEventSource.test.ts
@@ -0,0 +1,104 @@
+import assert from 'node:assert/strict';
+import { createServer, type Server } from 'node:http';
+import test from 'node:test';
+import { createAuthenticatedEventSource } from '../src/utils/authenticatedEventSource.ts';
+
+const listen = (server: Server): Promise<string> =>
+    new Promise((resolve) => {
+        server.listen(0, '127.0.0.1', () => {
+            const address = server.address();
+            if (!address || typeof address === 'string') throw new Error('Missing fixture listener');
+            resolve(`http://127.0.0.1:${address.port}`);
+        });
+    });
+const stop = (server: Server): Promise<void> =>
+    new Promise((resolve) => {
+        server.closeAllConnections();
+        server.close(() => resolve());
+    });
+
+void test(
+    'reconnects with header auth, omits ambient credentials and preserves named UTF-8 SSE events',
+    { timeout: 5_000 },
+    async () => {
+        const requests: Array<{ url: string; authorization: string | undefined; cookie: string | undefined }> = [];
+        const server = createServer((request, response) => {
+            requests.push({
+                url: request.url!,
+                authorization: request.headers.authorization,
+                cookie: request.headers.cookie,
+            });
+            response.writeHead(200, { 'content-type': 'text/event-stream' });
+            response.write(
+                `retry: 20\nevent: update\ndata: ${JSON.stringify({ value: '갱신', attempt: requests.length })}\n\n`
+            );
+            if (requests.length === 1) response.end();
+        });
+        const origin = await listen(server);
+        const source = createAuthenticatedEventSource(`${origin}/events?scope=tournament`, 'ga_synthetic-fixture');
+        try {
+            const events: unknown[] = [];
+            await new Promise<void>((resolve) =>
+                source.addEventListener('update', (event) => {
+                    events.push(JSON.parse(event.data));
+                    if (events.length === 2) resolve();
+                })
+            );
+            assert.deepEqual(events, [
+                { value: '갱신', attempt: 1 },
+                { value: '갱신', attempt: 2 },
+            ]);
+            assert.deepEqual(
+                requests,
+                Array.from({ length: 2 }, () => ({
+                    url: '/events?scope=tournament',
+                    authorization: 'Bearer ga_synthetic-fixture',
+                    cookie: undefined,
+                }))
+            );
+        } finally {
+            source.close();
+            await stop(server);
+        }
+    }
+);
+
+void test('401 is terminal and redirects never forward the authorization header', { timeout: 5_000 }, async () => {
+    let redirectedRequests = 0;
+    const target = createServer((_req, res) => {
+        redirectedRequests += 1;
+        res.writeHead(200);
+        res.end();
+    });
+    const targetOrigin = await listen(target);
+    const server = createServer((req, res) => {
+        res.writeHead(req.url === '/unauthorized' ? 401 : 302, { location: targetOrigin });
+        res.end();
+    });
+    const origin = await listen(server);
+    try {
+        for (const endpoint of ['unauthorized', 'redirect']) {
+            const source = createAuthenticatedEventSource(`${origin}/${endpoint}`, 'ga_synthetic-fixture');
+            try {
+                const code = await new Promise<number | undefined>((resolve) =>
+                    source.addEventListener('error', (event) => resolve(event.code))
+                );
+                if (endpoint === 'unauthorized') {
+                    assert.equal(code, 401);
+                    assert.equal(source.readyState, source.CLOSED);
+                }
+            } finally {
+                source.close();
+            }
+        }
+        assert.equal(redirectedRequests, 0);
+    } finally {
+        await stop(server);
+        await stop(target);
+    }
+});
+
+void test('rejects configured query or URL credentials before connecting', () => {
+    assert.throws(() => createAuthenticatedEventSource('http://localhost/events?token=synthetic', 'ga_synthetic'));
+    assert.throws(() => createAuthenticatedEventSource('http://user:synthetic@localhost/events', 'ga_synthetic'));
+});
diff --git a/app/gateway-api/src/server.ts b/app/gateway-api/src/server.ts
index 5e3a08cc..04273bcc 100644
--- a/app/gateway-api/src/server.ts
+++ b/app/gateway-api/src/server.ts
@@ -1,3 +1,4 @@
+import { safeHttpLoggerOptions, safeHttpErrorHandler } from '@sammo-ts/common';
 import fastify, { type FastifyRequest } from 'fastify';
 import cors from '@fastify/cors';
 import fastifyStatic from '@fastify/static';
@@ -89,9 +90,10 @@ export const createGatewayApiServer = async () => {
         config.defaultNavigationConfigFile
     );
     const app = fastify({
-        logger: true,
+        logger: safeHttpLoggerOptions,
         routerOptions: gatewayFastifyRouterOptions,
     });
+    app.setErrorHandler(safeHttpErrorHandler);
     const webPush = new WebPushCoordinator(
         postgres.prisma as GatewayPrismaClient,
         {
diff --git a/app/gateway-api/src/trpc.ts b/app/gateway-api/src/trpc.ts
index 315a247b..739369e5 100644
--- a/app/gateway-api/src/trpc.ts
+++ b/app/gateway-api/src/trpc.ts
@@ -1,8 +1,9 @@
+import { safeTrpcErrorFormatter } from '@sammo-ts/common';
 import { initTRPC } from '@trpc/server';
 
 import type { GatewayApiContext } from './context.js';
 
-const t = initTRPC.context<GatewayApiContext>().create();
+const t = initTRPC.context<GatewayApiContext>().create({ errorFormatter: safeTrpcErrorFormatter });
 
 export const router = t.router;
 export const procedure = t.procedure;
diff --git a/app/gateway-api/test/httpErrorPrivacy.test.ts b/app/gateway-api/test/httpErrorPrivacy.test.ts
new file mode 100644
index 00000000..4d20f567
--- /dev/null
+++ b/app/gateway-api/test/httpErrorPrivacy.test.ts
@@ -0,0 +1,51 @@
+import fastify from 'fastify';
+import { TRPCError } from '@trpc/server';
+import { fastifyTRPCPlugin } from '@trpc/server/adapters/fastify';
+import { describe, expect, it } from 'vitest';
+import { router as gatewayRouter, procedure as gatewayProcedure } from '../src/trpc.js';
+
+const internalFailure = () => {
+    throw new Error('synthetic-db-secret', { cause: new Error('synthetic-cause-secret') });
+};
+const badInput = () => {
+    throw new TRPCError({
+        code: 'BAD_REQUEST',
+        message: '잘못된 입력입니다.',
+        cause: new Error('synthetic-private-cause'),
+    });
+};
+
+describe('public HTTP error privacy', () => {
+    it('the real router factory hides internal errors and all stacks while preserving validation messages', async () => {
+        const app = fastify();
+        await app.register(fastifyTRPCPlugin, {
+            prefix: '/gateway',
+            trpcOptions: {
+                router: gatewayRouter({
+                    internal: gatewayProcedure.query(internalFailure),
+                    invalid: gatewayProcedure.query(badInput),
+                }),
+                createContext: () => ({}),
+            },
+        });
+        try {
+            const address = await app.listen({ host: '127.0.0.1', port: 0 });
+            for (const prefix of ['gateway']) {
+                for (const procedure of ['internal', 'invalid']) {
+                    const response = await fetch(`${address}/${prefix}/${procedure}`);
+                    const body = (await response.json()) as {
+                        error: { message: string; data: { code: string; stack?: string } };
+                    };
+                    expect(response.status).toBe(procedure === 'internal' ? 500 : 400);
+                    expect(body.error.message).toBe(
+                        procedure === 'internal' ? 'Internal server error' : '잘못된 입력입니다.'
+                    );
+                    expect(body.error.data.stack).toBeUndefined();
+                    expect(JSON.stringify(body)).not.toContain('synthetic-');
+                }
+            }
+        } finally {
+            await app.close();
+        }
+    });
+});
diff --git a/docs/release-operations.md b/docs/release-operations.md
index 07178123..32b1ed08 100644
--- a/docs/release-operations.md
+++ b/docs/release-operations.md
@@ -540,3 +540,29 @@ schema head·component 검사는 그대로 수행합니다.
 Local unit, 격리 DB integration과 fixture Chromium 통과는 운영 PM2, 외부
 Caddy/HTTPS, 방화벽과 실제 운영 DB 전환을 증명하지 않습니다. 운영 배포에서는
 위 확인 목록을 실제 서비스 경로에서 다시 수행해 주세요.
+
+## SSE 인증 전송과 API 진단 보안 (2026-10-09)
+
+게임 frontend의 SSE는 `eventsource@5.1.2`의 fetch adapter로
+`Authorization: Bearer`를 전달한다. URL에는 `scope=tournament` 같은 구독 선택만
+남기며 token, URL credential, ambient cookie, redirect 전달을 허용하지 않는다.
+기존 native EventSource를 사용하는 열린 탭은 새 game API에서 401을 받으므로
+배포 후 새로고침해야 한다. 독립 배포라면 새 frontend를 먼저 게시하고 game API를
+갱신한다. 새 frontend의 헤더 인증은 이전 game API도 지원한다. API만 먼저
+갱신하면 구형 탭의 실시간 갱신이 중단될 수 있다.
+
+SSE는 최초 요청과 매 frame 작업 전·전송 전에 Redis token, flush watermark,
+user/session/profile과 게임 접근 제재를 확인한다. 만료 타이머와 Gateway flush가
+대기 중인 연결을 닫고 Redis 장애는 fail closed로 처리한다. 연결별 대기 작업은
+32개, frame과 socket buffer는 64 KiB로 제한하고 slow consumer를 닫는다.
+재연결 뒤 메인은 기존 갱신 큐로 snapshot을 복구한다. 게임 계산·RNG·DB schema와
+read-model invalidation/grant의 사용자 범위는 변경하지 않는다. 연결 수 전체의
+상한이나 온라인 인증 rate limit까지 구현한 것으로 해석하지 않는다.
+
+Game/Gateway HTTP logger는 raw URL/query/header/body와 error message/cause/stack
+대신 static route, request ID, status와 허용된 error code만 남긴다. Fastify의
+기본 404/오류 message도 정화한다. 공개 tRPC 오류의 stack을 제거하고 내부 500의
+message는 일반 문구로 치환한다. 4xx의 사용자용 검증/권한 문구는 유지한다.
+이 정책은 HTTP API 로그의 범위이며 release builder의 관리자 build log를
+일괄 숨기지 않는다. 장애 조사 시 request ID·route·status·code와 별도 격리 재현을
+사용하며 운영 HTTP 로그에 credential이나 raw error payload를 다시 추가하지 않는다.
diff --git a/packages/common/src/http/errorPrivacy.ts b/packages/common/src/http/errorPrivacy.ts
new file mode 100644
index 00000000..50b091bc
--- /dev/null
+++ b/packages/common/src/http/errorPrivacy.ts
@@ -0,0 +1,31 @@
+/** Preserve public validation/permission messages while hiding internal causes and stacks. */
+export const safeTrpcErrorFormatter = <T extends { message: string; data: { code: string; stack?: string } }>({
+    shape,
+}: {
+    shape: T;
+}): T => ({
+    ...shape,
+    message: shape.data.code === 'INTERNAL_SERVER_ERROR' ? 'Internal server error' : shape.message,
+    data: { ...shape.data, stack: undefined },
+});
+
+export const safeHttpErrorHandler = (
+    error: unknown,
+    request: { log: { error: (context: object, message: string) => void } },
+    reply: { code: (status: number) => { send: (body: object) => unknown } }
+): void => {
+    const value = error && typeof error === 'object' ? (error as { statusCode?: number; message?: string }) : {};
+    const status =
+        typeof value.statusCode === 'number' &&
+        Number.isInteger(value.statusCode) &&
+        value.statusCode >= 400 &&
+        value.statusCode < 500
+            ? value.statusCode
+            : 500;
+    request.log.error({ err: error }, 'Request handling failed');
+    reply.code(status).send({
+        statusCode: status,
+        error: status >= 500 ? 'Internal Server Error' : 'Request Error',
+        message: status >= 500 ? 'Internal server error' : (value.message ?? 'Request failed'),
+    });
+};
diff --git a/packages/common/src/http/safeLogger.ts b/packages/common/src/http/safeLogger.ts
new file mode 100644
index 00000000..6b9ea512
--- /dev/null
+++ b/packages/common/src/http/safeLogger.ts
@@ -0,0 +1,75 @@
+const errorCodes = /^(?:P\d{4}|FST_ERR_[A-Z_]+|ERR_[A-Z_]+|UNAUTHORIZED|FORBIDDEN|BAD_REQUEST|INTERNAL_SERVER_ERROR)$/;
+
+const errorSummary = (
+    error: unknown
+): { type: string; message: string; stack: string; code?: string; statusCode?: number } => {
+    const value = error && typeof error === 'object' ? (error as Record<string, unknown>) : {};
+    const code =
+        typeof value.code === 'string' && value.code.length < 80 && errorCodes.test(value.code)
+            ? value.code
+            : undefined;
+    const statusCode =
+        typeof value.statusCode === 'number' && value.statusCode >= 400 && value.statusCode <= 599
+            ? value.statusCode
+            : undefined;
+    return {
+        type: 'RequestError',
+        message: 'Request handling failed',
+        stack: '',
+        ...(code ? { code } : {}),
+        ...(statusCode ? { statusCode } : {}),
+    };
+};
+
+/** HTTP diagnostics carry static route/status/code, never credentials or error payloads. */
+export const safeHttpLoggerOptions = {
+    serializers: {
+        req: (request: { method?: string; routeOptions?: { url?: string } }) => ({
+            method: request.method,
+            // URLs can carry OAuth/session/input values, including unmatched path segments.
+            url: request.routeOptions?.url ?? '[unmatched]',
+        }),
+        res: (response: { statusCode?: number }) => ({ statusCode: response.statusCode }),
+        err: errorSummary,
+    },
+    redact: {
+        paths: [
+            'authorization',
+            'cookie',
+            'password',
+            'sessionToken',
+            'accessToken',
+            'token',
+            'secret',
+            'body',
+            'headers',
+            'req.headers',
+            'req.body',
+            'res.headers',
+        ],
+        remove: true,
+    },
+    hooks: {
+        logMethod(args: unknown[], method: (...values: unknown[]) => void): void {
+            const first = args[0];
+            const error =
+                first instanceof Error
+                    ? first
+                    : first && typeof first === 'object' && 'err' in first
+                      ? first.err
+                      : undefined;
+            if (error !== undefined) {
+                // Fastify also copies err.message into msg; serializers alone do not protect it.
+                method.apply(this, [{ err: errorSummary(error) }, 'Request handling failed']);
+            } else {
+                // Fastify's default 404 handler also embeds the raw URL in a message.
+                method.apply(
+                    this,
+                    args.map((value) =>
+                        typeof value === 'string' && /^Route .+ not found$/.test(value) ? 'Route not found' : value
+                    )
+                );
+            }
+        },
+    },
+};
diff --git a/packages/common/src/index.ts b/packages/common/src/index.ts
index 6a2e9d0f..4b7616c3 100644
--- a/packages/common/src/index.ts
+++ b/packages/common/src/index.ts
@@ -31,6 +31,8 @@ export * from './gateway/profileStatus.js';
 export * from './gateway/runtimeDiagnostics.js';
 export * from './game/accessPenalty.js';
 export * from './http/trpcTransport.js';
+export * from './http/safeLogger.js';
+export * from './http/errorPrivacy.js';
 export * from './webPush/types.js';
 export { canReadPlayAudit, canReadPlayAuditAccounts } from './auth/playAudit.js';
 
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 44aa10b1..f0e652cf 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -381,6 +381,9 @@ importers:
       es-toolkit:
         specifier: ^1.43.0
         version: 1.51.0
+      eventsource:
+        specifier: 5.1.2
+        version: 5.1.2
       mitt:
         specifier: ^3.0.1
         version: 3.0.1
@@ -3750,6 +3753,14 @@ packages:
   eventemitter2@6.4.9:
     resolution: {integrity: sha512-JEPTiaOt9f04oa6NOkc4aH+nVp5I3wEjpHbIPqfgCdD5v5bUzy7xQqwcVO2aDQgOWhI28da57HksMrzK9HlRxg==}
 
+  eventsource-parser@4.1.1:
+    resolution: {integrity: sha512-zaWNqeSLeyzEAAt2Q6aDBRDRk/VnPmsKqvToyGvv6aahvLv71A4Jw7jG93Hckf11zXurbqgsffvpSgKPoeU1Qw==}
+    engines: {node: '>=22.12'}
+
+  eventsource@5.1.2:
+    resolution: {integrity: sha512-VJnwqqp+fOT3WDkjnUy49Zuyh48+kH0JdJApZkslrRQyx35zIZJeJYJl0+a+LrTzh5TFv6MdmXnBDv71UXFyWQ==}
+    engines: {node: '>=22.12.0'}
+
   expect-type@1.4.0:
     resolution: {integrity: sha512-KfYbmpRm0VbLjEvVa9yGwCi9GI34xvi7A/HXYWQO65CSD2u3MczUJSuwXKFIxlGsgBQizV9q5J9NHj4VG0n+pA==}
     engines: {node: '>=12.0.0'}
@@ -7879,6 +7890,12 @@ snapshots:
 
   eventemitter2@6.4.9: {}
 
+  eventsource-parser@4.1.1: {}
+
+  eventsource@5.1.2:
+    dependencies:
+      eventsource-parser: 4.1.1
+
   expect-type@1.4.0: {}
 
   exsolve@1.0.8: {}